1. Field
Power driven dental scalers are well known. Of particular interest herein are those dental scalers driven by means of a fluid exiting through outlet ports in a shaft and impinging upon a rotor disposed on the shaft to impart vibrational movement to the shaft.
2. State of the Art
Of the power driven dental scalers currently available, most common are scalers utilizing a flow of compressed air or an electrical ultronsonic transducer to cause a scraping-type work tool to vibrate.
Typical of the earlier air-driven dental scalers are those of U.S. Pat. Nos. 3,820,529 and 3,444,622 to Miles et al, which scalers utilize an air-driven ball contained in a chamber. Movement of the ball against the walls of the chamber imparts vibration to the chamber which vibrations are then transmitted to the scraping tool.
A more recent type of air-driven scaler, described in U.S. Pat. No. 3,526,962 to Fuerst, utilizes a rotatable mandrel which has an irregularly-shaped tip engaged with a reciprocal block in which the mandrel tip is received.
It is characteristically a problem of these air driven scaler that much of the vibrational energy generated by the vibrator motor is transferred to the handle portion of the dental scaler rather than to the scraper tool. Moreover, the modes of vibration of these scalers may change as moving parts of the vibration generating mechanism wear with time.
In U.S. Pat. No. 3,703,037 to Robinson, there is described a dental scaler which utilizes an electrical ultrasonic transducer to provide constant modes of vibration for coupling with particular types of work tools. One disadvantage of the ultrasonic scaler, however, is the cost of the transducer and its associated ultrasonic generator.
A recent improvement in air-driven dental scalers is disclosed in U.S. Pat. No. Re. 29,687 to Sertich. This dental scaler has very few moving parts as compared to the aforementioned mechanically complicated air-driven scalers and provides efficient transfer of vibrational energy to a scraping-type work tool with relatively little vibration being transferred to the handle portion of the instrument. The Sertich-type scaler provides uniform modes of constant vibration which may be matched with the vibratory modes of various types of work tools without the need for any complicated electronic components.
The Sertich-type scaler utilizes a rotor disposed on a shaft which is driven by a fluid media such as air to propel the rotor rotatably about the shaft and impart vibratory motion thereto. The rotor and the outside surface of the shaft provide a gap into which air flow occurs through outlet ports dispoded in the wall of the shaft beneath the rotor. The air impinges on the inner surface of the rotor causing it to rotate about the shaft in a manner which creates a vibrational movement in the shaft which is transmitted to a work tool connected to the shaft. In order to operate properly, it is necessary that the rotor remain disposed over the air outlet ports on the shaft, and in order to obtain maximum efficiency, it is necessary to have the rotor rotate freely about the shaft at a position centralized axially over the air outlet ports. Rotation of the rotor about the shaft tends to create wear on the outside surface of the shaft. That wear can induce a pattern of unequal fluid flow out of the space defined by the ends of the rotor and the shaft. The corresponding pressure differentials set up at the ends of the rotor can cause the rotor to be displaced from its position over the outlet ports, which greatly decreases the efficiency of operation of the device. Accordingly, there is a need for a means for compensating for wear induced by the rotor on the shaft surface and for continuously correcting axial displacement of the rotor from a centralized position above the outlet ports on the shaft.
An aspect of mechanical vibratory devices is that they tend to operate at certain well-defined frequencies. Those frequencies are influenced by the particular mass distribution along the shaft of the device and the location of the support means for the shaft. It has heretofore been unappreciated that not only is the location of the support means on the shaft important for determining the resultant vibrational frequencies at which the device operates, but that the particular resilient characteristics of the support means can be critical in determining and defining an operating frequency which maximizes scaling efficiency, without creating a need for a substantial increase in power input to move from one mode of resonance to the next. Accordingly, there has been a need for a vibrating device which utilizes particular support means for optimizing the power output of the vibrating device.